Invasion of Drosophila virilis by the Penelope transposable element

The Penelope family of transposable elements (TEs) is broadly distributed i n most species of the virilis species group of Drosophila. This element pla ys a pivot al role in hybrid dysgenesis in Drosophila virilis, in which at least four additional TE families are also activated. Here we present evide nce that the Penelope family of elements has recently invaded D. virilis. T his evidence includes: (1) a patchy geographical distribution, (2) genomic locations mainly restricted to euchromatic chromosome arms in various geogr aphical strains, and (3) a high level of nucleotide similarity among member s of the family. Two samples from a Tashkent (Middle Asia) population of D. virilis provide further support for the invasion hypothesis. The 1968 Tash kent strain is free of Penelope sequences, but all individuals collected fr om a 1997 population carry at least five Penelope copies. Furthermore, a se cond TE, Ulysses, has amplified and spread in this population. These result s provide evidence for the Penelope invasion of a D. virilis natural popula tion and the mobilization of unrelated resident transposons following the i nvasion.